Warren Chandler says four cars carrying anhydrous ammonia derailed upright on Wednesday at the supper hour.
He says the tank cars are intact and there are no leaks or any injuries.
He also says there is no threat to the public.
Community officials ordered a voluntary evacuation of about 150 homes closest to the derailment.
The company expects it will take a full day for workers to get the cars back on the tracks.Story continues after slideshow
"At that point, we were erring on the side of caution," he explained. "We hadn't heard from CN and our fire resources on the site thought it was best to do that in the event that something untoward should occur."
He said although the order was voluntary, most of the people in those homes did leave.
"We did have a few people check into our response centre," he said. "I would suspect for the others they dispersed locally in the community to friends and neighbours."
He said officials were satisfied with the rail company's response and felt the incident was properly handled, but admitted things were tense in the early going.
"You know, top of mind is rail safety in our communities these days. Until we have good contact with the rail provider on site and understand the situation a little better, it's always nerve-wracking."
Sexsmith is located 280 kilometres north of Edmonton and has a population of about 2,400 people.
Rail safety has been a contentious political topic since the derailment this summer in Lac-Megantic, Que., that killed 47 people.
Provincial transport ministers and municipalities have demanded greater transparency about what hazardous materials trains are carrying through Canadian communities.
However, the federal government has made no move to force rail companies to specify the cargo they carry.